1. Field of the Invention
The present invention relates generally to multilevel interconnections formed in integrated circuits (ICs) employing spin-on-glass planarization.
2. Description of the Related Art
Spin-on-glasses typically crack when hard-cured in cavities of aspect ratio greater than one due to tensile brittle fracture induced by shrinkage. This is especially true when the spin-on-glass (SOG) is subjected to later thermal shock and cycling. It is also especially true when the spin-on-glass is not fully encapsulated by other CVD-based oxides. This is unfortunate, since such encapsulation is cost-intensive and defect-prone. To avoid this problem, aspect ratios must be kept to .ltoreq.1 to provide acceptable process yields and process margins. Frequently, double spins of SOG and even interleaved chemical vapor depositions (CVD) between SOG spins are required to approach an SOG aspect ratio (height/width) of 1 or greater. This has the effect of minimizing the maximum shrinkage and thus the maximum stress and thus the cracking tendency. Such elaborate measures increase the process cost, and they still limit device packing density, which could benefit by aspect ratios of 2 to 3 which are beyond the reach of such measures.